For a switch-type converter, a constant on time control mode can be adopted in order to achieve a higher power factor. This is because a proportion factor of an input current and an input voltage is in direct proportion to a ratio of a square value of an on time and a switching period. Thus, once the on time is fixed, the input current may follow the input voltage when the switching period changes slightly in a full power frequency cycle, so as to obtain a relatively high power factor correction (PFC). Therefore, constant on time controlled converter are widely used in many power factor regulating applications.